The present invention relates in general to an inhalation device, and more particularly, to such a device for use with a cartridge having an outlet valve mechanism from which a medicant contained in the cartridge may be discharged in metered dosages in the form of an aerosol.
More than 21 million individuals in the United States suffer from asthma, chronic bronchitis or emphysema, and at least 5.25 million of them regularly use a metered dose inhaler (MDI). The use of MDIs is recognized as one of the most effective methods for the treatment of these and other respiratory problems. Physicians are considering the issues of compliance for typical MDIs and are prescribing enhancement devices for these MDIs or are specifying MDIs with features that improve drug inhalation technique and efficacy.
The majority of the medication dispersed from an MDI does not reach the lungs, but is deposited on the linings of the mouth and upper respiratory track. Seventy percent of the medication is typically lost by inelastic collision of the large mass and high velocity particles with the interior walls. Aerosols reaching the lungs have been known to have particles ranging in size from 2.5 to 5.5 um. With normal breathing, 50% of the medication reaching the lungs is often exhaled. When one's breath is held, time is allowed for the slower moving particles to impact the lung walls and to be retained, resulting in only about 10% of the medication being exhaled. The holding of one's breath is often impossible during, for example, an asthmatic attack.
MDI aerosols are inherently large momentum particles due both to their size and speed, as opposed to the optimum fine mist desired. The particles exiting from the pressurized medication containing cartridge have a size typically in the range of from 20 to 50 um. The large particle size is due to incomplete vaporization of the propellent, with the factors of temperature, concentration and time playing important rolls. Adiabatic expansion of the propellent cools the particles thereby competing against the formulation of the fine mist desired. The vapor is initially saturated thereby increasing the time for the particles to evaporate. The vaporization time can range from 0.3 msec for a dilute vapor to 0.8 sec for a saturated vapor. The propellent pressure is considered to play only a minor roll in particle size. For example, increasing the pressure from 45 to 80 PSI, decreases the particle size only from 3.7 to 2.2 um. Thus, known MDIs are generally inefficient and ineffective in converting the medication into a fine mist of particles that can be deposited in the proper bronchial area to relieve an asthmatic attack.
Devices that administer the proper amount of medication to specific locations of the lower respiratory system paired with drugs that are specially prepared and packaged to optimize the device are known, for example, from Hanson et al., U.S. Pat. No. 3,565,070, Thompson et al., U.S. Pat. No. 3,732,864, Warren, U.S. Pat. No. 3,814,297, Warren, U.S. Pat. No. 3,826,413, Young et al., U.S. Pat. No. 4,414,972 and Waters, IV et al., U.S. Pat. No. 4,592,348. Although these devices provide a convenient and effective MDI system, they must be used correctly in order to obtain an effective dosage. As the MDI aerosol is dispensed under pressure as a single shot, it is required that the user time each breath with the MDI aerosol discharge. The full dose of medication will frequently not be delivered deep within one's lungs if this timing is not synchronized. In addition, for those reasons previously discussed, only a small portion of the MDI aerosol is retained on the lung walls.
In order to increase the efficiency of these known MDIs, auxiliary devices have been designed to perform two pharmalogical functions, namely, reduction of medication deposited in the upper airways and increasing the medication deposited in the lungs. These auxiliary devices are known from Nowacki et al., U.S. Pat. No. 4,534,343, Sackner et al., U.S. Pat. No. 4,484,577 and Nowacki et al., U.S. Pat. No. 4,470,412, which provide a confined volume between the MDI and the users mouth. The large momentum particles are deposited in the auxiliary device instead of the upper airways of the user. It is the object of these auxiliary devices to improve drug delivery to the lungs by allowing the particles time to vaporize, in addition to providing more smaller particles having lower velocities. These for momentum particles can then follow the airflow through the upper airways and into the users lungs. There is still, however, the need for improvements in these MDIs and auxiliary devices to enhance their compactness, efficiency of operation and ease of use. In particular, there is the need to improve and simplify the mechanism for discharging the medication from the cartridge when the MDI is being used by children, elderly individuals and those with coordination problems.